When a cinema video is displayed on a television that complies with the National Television System Committee (NTSC) standards (e.g., in Japan and the USA) or when a cinema video recorded on a digital versatile disc (DVD) is displayed using an NTSC signal on a television, a 24-frame progressive video, i.e., a cinema video, is converted into a 60-field interlaced video, i.e., a telecine video.
This type of conversion is called the 2:3 pulldown process, in which a field before two fields is repeated once in a 5-field cycle (hereinafter, “repeat field”). Specifically, the same field is repeated once in the 5-field cycle, so that a video with a frame frequency 5/4 times as high as before is produced.
The telecine video is designed to be displayed on an interlaced display such as a cathode ray tube (CRT); therefore, when the telecine video is displayed on a 60-field interlaced display, the video is directly output thereto. However, in recent years, video is often displayed on a progressive display, such as a liquid crystal display television and a plasma television. To display the interlaced video on the progressive display, the interlaced video is subjected to deinterlace so that it is displayed as a progressive video.
Examples of deinterlace include a method of obtaining a single frame by combining the top field and the bottom field of interlace video. When the interlaced video to be converted is a telecine video that is obtained by the 2:3 pulldown process, in other words, when 60-frame interlaced video which is produced from 24-frame progressive video is converted into a 60-frame progressive video, it is preferable to combine the top field and the bottom field that are produced from a single frame of the 24-frame progressive video.
A typical conventional method is so-called film mode detection that detects whether the interlace video is a telecine video. A known method of performing film mode detection, i.e., 2:3 pulldown sequence detection, from the interlaced scanning video is a technique in which the sum of absolute differences between frames (a feature value) with respect to the image of the current field and the image of the second field prior to the current field is calculated in pixel units, and film detection/non-detection is performed by using a characteristic in which the field having high correlation is repeated once in the 5-field cycle (see, for example, Japanese Laid-open Patent Publication No. 2007-300152). Because the repeat field is detected in this way, the top field and the bottom field can be properly combined using the deinterlace.
In typical processing for deinterlace, when a film mode is detected and when the timing of the occurrence of the repeat field is determined, the deinterlace is performed, while maintaining the film mode, assuming that the repeat field is cyclically repeated. However, for example, in a process of producing a commercial video for publicity, although the commercial video is produced preferably by editing the cinema video and then converting the edited cinema video to the telecine video, most commercial videos are produced by editing the telecine video. Therefore, the 5-field cycle becomes irregular in some parts.
Because the 5-field cycle is occasionally disrupted in the edited interlaced cinema video, when detecting the film mode using the above-described method and performing the deinterlace by combining the fields based on a detection result, video images located on both sides of an editing point are combined in some cases. When the video images located on both sides of the editing point are combined in this way, the 60-progressive frame is produced by combining the top field and the bottom field obtained from different fields of the telecine video, which causes combing artifacts.